// 参考 https://github.com/darknessomi/musicbox/wiki/
const crypto = require('crypto')
const bigInt = require('big-integer')
const modulus = '00e0b509f6259df8642dbc35662901477df22677ec152b5ff68ace615bb7b725152b3ab17a876aea8a5aa76d2e417629ec4ee341f56135fccf695280104e0312ecbda92557c93870114af6c9d05c4f7f0c3685b7a46bee255932575cce10b424d813cfe4875d3e82047b97ddef52741d546b8e289dc6935b3ece0462db0a22b8e7'
const nonce = '0CoJUm6Qyw8W8jud'
const pubKey = '010001'

String.prototype.hexEncode = function() {
    let hex, i

    let result = ""
    for (i = 0; i < this.length; i++) {
        hex = this.charCodeAt(i).toString(16)
        result += ("" + hex).slice(-4)
    }
    return result
}

const createSecretKey = (size) => {
    const keys = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
    let key = ""
    for (let i = 0; i < size; i++) {
        let pos = Math.random() * keys.length
        pos = Math.floor(pos)
        key = key + keys.charAt(pos)
    }
    return key
}

const aesEncrypt = (text, secKey) => {
    const _text = text
    const lv = new Buffer('0102030405060708', "binary")
    const _secKey = new Buffer(secKey, "binary")
    const cipher = crypto.createCipheriv('AES-128-CBC', _secKey, lv)
    let encrypted = cipher.update(_text, 'utf8', 'base64')
    encrypted += cipher.final('base64')
    return encrypted
}

const zfill = (str, size) => {
    while (str.length < size) str = "0" + str
    return str
}

const rsaEncrypt = (text, pubKey, modulus) => {
    const _text = text.split('').reverse().join('')
    const biText = bigInt(new Buffer(_text).toString('hex'), 16),
        biEx = bigInt(pubKey, 16),
        biMod = bigInt(modulus, 16),
        biRet = biText.modPow(biEx, biMod)
    return zfill(biRet.toString(16), 256)
}

const encrypt = (params) => {
    const text = JSON.stringify(params)
    const secKey = createSecretKey(16)
    const encText = aesEncrypt(aesEncrypt(text, nonce), secKey)
    const encSecKey = rsaEncrypt(secKey, pubKey, modulus)
    return {
        params: encText,
        encSecKey: encSecKey
    }
}

module.exports = encrypt